Genetic variation in the envelope gene and slow onset of clinical disease characterize lentivirus infections. Variants isolated late in infection are generally cytopathic in vitro and, in animal experiments, more pathogenic in vivo than the parent virus. Many defects in immune cell function are evident, however, during asymptomatic periods and may be essential factors in overall disease progression. At these early time points post-infection, virus is sequestered and replicating in lymph nodes but not in peripheral blood lymphocytes. Lymph nodes may, therefore, harbor a population of variant viruses functionally significant to viral pathogenesis. In this proposal, variants from lymph nodes and peripheral blood lymphocytes of preclinical SIVMne infected macaques will be analyzed and the functional properties conferred on gp120 by env mutations of these variants determined. Identification of early variant viruses with specific functional capabilities will be valuable in designing therapeutic intervention for early seroconverters. The specific aims are as follows: AIM 1: To determine the temporal relationship between SIV variants arising in lymph node to those found in PBMC of macaques infected with a molecular clone of SIVMne. DNA from lymph node and peripheral blood lymphocytes of SIV- infected macaques will be analyzed by PCR cloning of env. AIM 2: To construct chimeric viruses containing representative early variant gp120. Variant env sequences that are specific to lymph node or peripheral blood lymphocytes or that arise early in infection will be used to construct variant env-SIVMne chimeras. AIM 3: To determine the effect of env mutations on functional activity of gp120. Env-specific chimeras will be evaluated for the functional properties of receptor binding, cell activation and cell protein co-localization.